Hydrogen peroxide, which has germ-killing, cleaning, bleaching and disinfecting activities, is in general utilized in the disinfectant of contact lenses and in the bleaching agent of textile materials, and also recognized as a legal food additive. However, hydrogen peroxide is known to have the tendency to generate free oxygen having high reactivity, the strong oxidizing effect of which will cause proteins to denature. Hence, after the disinfecting operation of contact lenses or the bleaching procedure of textile materials using hydrogen peroxide, the residual hydrogen peroxide must be subsequently decomposed to avoid the undesired injury caused to users.
For this purpose, skilled artisans often use catalases to decompose hydrogen peroxide residues, which also is generally recognized as the most efficient method. For example, U.S. Pat. Nos. 4,585,488, 5,145,644, 5,362,647 and 5,521,091 disclose methods for the destruction of the hydrogen peroxide remaining in the disinfectant of contact lenses in which a catalase is added during the disinfecting operation. In addition, GB 2216149 and JP-A-104781 teach that, after bleached with hydrogen peroxide, textile substrates should be further treated with a catalase to destroy the hydrogen peroxide residues prior to the dyeing step.
Catalases [hydrogen peroxide oxidoreductases (EC 1.11.1.6)] are enzymes which catalyze the conversion of two molecules of hydrogen peroxide (H.sub.2 O.sub.2) to one molecule of oxygen (O.sub.2) through oxidation and two molecules of water (H.sub.2 O) through reduction. The catalysis reaction is as follows: ##STR1##
Catalases are present in certain animal, plant and microorganism cells, and are the required enzymes for these cells to survive in the aerobic environment. At present almost all the catalases available are obtained by purification from such cells, and among which the catalase derived from bovine livers, in particular, has been the most preferred one for the above mentioned purposes. However, in 1990, a chronic viral disease known as BSE (bovine spongiform encephalopathy) out-broke in European cattle herds. Recent studies have shown that human may be infected with this disease [Dellar and Lacey 1991 Nutr. Health (Bicester) 7:117-134; Dealler and Lacey 1990 Food Microbiol. 7:253-280). It arouses interests in finding non-mammalian-derived catalases, such as those derived from microorganism sources, instead of bovine liver catalases for the industrial applications.
Microorganisms which have been employed to obtain catalase preparations through fermentation include Aspergillus niger, Penicillium notatutn, Micrococcus luteus, etc. For instance, U.S. Pat. No. 3,123,539 discloses catalases derived from fungi such as Aspergillus niger and Penicillium notatum; U.S. Pat. No. 2,635,069 and 5,360,732 and WO 93/17721 disclose catalases generated from Aspergillus niger; and U.S. Pat. No. 5,521,091 discloses catalases derived from Micrococcus luteus and Aspergillus niger. The catalases taught in the above patents are prepared by conventional methods including fermenting microorganisms, breaking cell bodies, and then purifying crude extract.
Nevertheless, the yields of catalases prepared from such fermentation methods are not satisfactory. For example, U.S. Pat. No. 3,123,539 discloses that the 1000 g protein product recovered from the cell bodies of Micrococcus luteus (wet weight 95 pounds) yields only 5% of catalase; and U.S. Pat. No. 2,635,069 teaches that each gram crude protein extract obtained from the action of Aspergillus niger has only 2.4 units of catalase activity. For the sake of improving catalase yield, U.S. Pat. No. 5,360,732 tries to produce novel strains of Aspergillus niger, and the resulted catalytic activity is 14.17 units per milligram crude protein extract. According to the data shown in Table 1 of WO 93/17721, the specific activity of Aspergillus niger is about 7.5 units per microgram. It is calculated that the above 14.17 units of activity is performed by 1.9 .mu.g catalase. In other words, the crude protein extract obtained in U.S. Pat. No. 5,360,732 contains less than 0.2% catalases.
Shuichi Furuta and Hiroaki Hayashi disclose in J. Biochem. 107:708-713 (1990) the expression of a recombinant catalase gene using genetic engineering technology. However, the produced catalase was not high in yield, merely 16 mg/4L before farther purification.
In view of the above, there continues to be a need for improving the catalase now employed in the art, both in its source and its preparation.